There are various types of mobile radio networks with which mobile related services can be provided to mobile user equipment. For example, Global System for Mobiles (GSM) networks provide a facility for data and voice communications via fixed capacity radio communications channels. The Universal Mobile Telecommunications System (UMTS) on the other hand provides improved flexibility in affording greater data rates to mobile user equipment whilst still providing a roaming facility made possible by a cellular architecture. On the other hand the Wireless Local Area Networks (WLAN) standards for example IEEE 802.11B referred to as WIFI provide a facility for high data rate communications within so called WLAN hotspots. Such WLANs provide a substantially greater data rate than can be provided through cellular mobile radio architectures such as GSM and UMTS. Furthermore, WLANs are often unregulated in that a single mobile user can occupy a greater proportion of the available data communications bandwidth than another mobile user.
Many applications utilize an internet protocol to support data communication such as for example multi-media services. As such, a communication service may be provided by communicating internet protocol packets via a variety of different networks. The application may not be aware of the type of network via which the internet protocol packets are being communicated. Thus, in the case of wireless communications the application may communicate internet packets via either a GSM network or a WLAN. However, since these different types of mobile radio networks offer substantially different communications bandwidths, a quality of service which can be supported will be different in accordance with the communications bandwidth provided by the mobile access network. As such, a communications service may be provided using different communications session levels, each level providing a different quality of service as determined by the access network via which the mobile node is currently communicating. For each communications session level, different types of media may be communicated. Thus for example, for one communications session level video may be supported, whereas another level may only support audio.
European patent EP 1 435 748 discloses a telecommunications system in which a mobility manager is arranged to in form an applications server providing a communications service to a mobile node of a pending or completed change of affiliation of the mobile node from one access network to another. The application server can therefore change a communications session level before or after the change of affiliation depending on whether there is an increase or a decrease in communications session level. The communications session levels provide different a service qualities, which can support different types of media. The application server can therefore adapt the communications session level to the effect of maintaining at least one service to which a user has subscribed. In order to determine when a change of affiliation may occur, the mobility manager receives access network evaluation messages from access gateways of the mobile access networks concerned, to identify when a hand-over may occur.